1. Field of the Invention
The present invention generally relates to an image reading apparatus for reading an image of a document sheet for use in a copying machine or the like, and more particularly, to an image reading apparatus of the above-described type which is capable of reading also an image of a photographic film.
2. Description of Related Art
Recently, a digital copying apparatus capable of storing and processing informations of an image of a read-out document as an electric signal has been put into practical use.
In such a copying apparatus as referred to above, a normal photographic film, that is, a negative film has easily been polarized into positive, which fact has raised a great demand to directly have a copied object from the photographic film. In Japanese Patent Application Laid-Open No. 59-198439 (1984), there is disclosed one such copying apparatus whereby an enlarged object from a small light-permeable document, for example, a photographic film or the like is obtained. This copying apparatus is of such construction that a projector, a reflecting mirror and the like are additionally provided in a copying machine which exposes a film by scanning a document sheet on a document platen by the use of an optical system. The projector enlarges and projects an image of the film from the lateral side. The projected image is reflected onto the document platen through the reflecting mirror and then read by the optical scanning system.
Although the above-mentioned conventional copying apparatus is capable of enlarging and reading a photographic film, it has disadvantages as will be described below.
The conventional apparatus requires more space for an optical path so as to enlarge and project the image of the film, resulting consequently in a bulky structure of the whole apparatus. When the image of the film is read, since the projected image is read through an unnecessary document platen, efficient illumination can not be obtained because of a loss of a light quantity. Projecting the whole of the image consumes great electricity in a light source. Furthermore, when the image of the film is read, the apparatus necessitates the aforementioned optical members to be mounted on the document platen.
Since illumination of the projected image on the document platen is decreased from the center to the periphery thereof, it is necessary to adjust and compensate the reading part both in a main-scanning direction and in a sub-scanning direction, respectively, in order to obtain uniform illumination.
If the projected image onto the document platen is not exactly focused with respect to the reading part, the image can not read with great accuracy. Heretofore, in order to perform focusing, an operator has moved a reflecting lens of the projector in the direction of an optical axis while watching the projected image. This, however, takes much time and the obtained focus is not necessarily met because it depends on a decision of the operator.